This invention relates to a method and a device for power reduction of jammer signals received by the sidelobes of a radar antenna. As a rule, these signals are continuous or chopped active-jamming signals transmitted by a number of independent jammers and are received by the sidelobes of the radar antenna. The level of the signals is such that they are considered as real signals which originate from targets and completely disturb the operation of the radar.
In order to guard against active jamming of this type, the countermeasure known as sidelobe cancellation (SLC) has been proposed. A description of this technique may be found in an article by M. A. Johnson and D. C. Stoner "ECCM from the radar designer's viewpoint" published in the Microwave Journal, March 1978 issue, pages 59 and 60.
According to this technique, a number N of auxiliary antennas associated with N reception channels is employed in addition to the radar antenna and its corresponding processing channel. A weighted linear combination of the N complex signals delivered by the N auxiliary channels is formed and subtracted from the signal of the main channel, the weighting coefficients being determined from the signals received on the auxiliary channels in order to reduce the resultant jamming power on the main channel.
However, the effectiveness of the method outlined in the foregoing is evidently based on the determination of the gains relative to the jamming signals achieved by each auxiliary channel with respect to the gain of the main channel. It is observed under these conditions that any signal other than the jamming signals proper (i.e. thermal noise, clutter echoes, useful echoes) must also be considered as a clutter signal which has the effect of interfering with precise determination of the weighting coefficients and consequently impairs the quality of jamming suppression. Consequently in devices employed in the prior art, the measurement of weighting coefficients is such that the effective presence on the one hand of jamming and on the other hand of the above-defined clutter signals in the range gates forming "boxcars" or range cells which are chopped in the radar pulse-repetition periods is not taken into account. The weighting coefficients are therefore computed in an inaccurate manner.